Tracking fiber optic wafer concentrator

ABSTRACT

A solar power system for supplying concentrated solar energy. The system includes a cylindrical absorber tube carrying the working fluid and a concentrator assembly, which includes an array of linear lenses such as Fresnel lenses. The concentrator assembly includes a planar optical wafer paired with each of the linear lenses to direct light, which the lenses focus on a first edge of the wafers, onto the collector via a second or output edge of the wafers. Each of the optical wafers is formed from a light transmissive material and acts as a light “pipe.” The lens array is spaced apart a distance from the first edges of the optical wafers. This distance or lens array height is periodically adjusted to account for seasonal changes in the Sun&#39;s position, such that the focal point of each linear lens remains upon the first edge of one of the optical wafers yearlong.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/888,584, filed Sep. 23, 2010, which claims the benefit of U.S.Provisional Application No. 61/245,507 filed Sep. 24, 2009, both ofwhich are incorporated herein by reference in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, in general, to concentrators for use inthe solar power industry, and, more particularly, to systems, devicesand methods for more effectively concentrating solar energy (or, moresimply, for concentrating sunlight) using an improved trackingconcentrator such as a fiber optic wafer concentrator adapted foreffective tracking of the Sun.

2. Relevant Background

In general, concentrated solar power systems use lenses or mirrors tofocus a large area of sunlight onto a small area. Electrical power isproduced when the concentrated light is directed onto photovoltaicsurfaces or when the concentrated light is used to heat a transfer fluidfor a conventional power plant (e.g., to run a turbine with steam).

With regard to the latter example, thermal concentrators have beenaround for many years, with concentrated solar thermal (CST) being usedto produce renewable heat or electricity (which may be labeledthermoelectricity as it is usually generated via steam generation). Awide range of concentrating technologies exists with a parabolic troughbeing a popular choice for use in many CST systems. A parabolic troughincludes a linear parabolic reflector that concentrates light onto areceiver that is positioned along the reflector's focal line. Thereceiver is typically a pipe or tube (i.e., is an absorber tube)positioned directly above the middle of the parabolic reflector (ormirrored surface that may be a coating of silver, polished aluminum, orthe like). The pipe or tube is filled with a working or transfer fluid.The reflector is operated to attempt to accurately track the Sun'smovements during daylight hours by tracking along a single axis. In somecases, the working fluid is an oil, a molten salt, or other materialthat is heated to high temperatures (300 to 700° F.) as it flows throughthe receiver, and fluid is then used as a heat source for a powergeneration system (e.g., to heat water to create steam that is used toturn a turbine generator or the like).

There is a strong desire to expand the use of renewable energy sourcessuch as thermal concentrators. As discussed above, CST systems generallytrack the Sun east to west from the morning to evening hours, and thisis done with a complex tracking system that tilts a linear parabolicconcentrator or reflector, which may be may several hundred meters longand up to as much as ten or meters across. Generally, the lines or solarfiled piping/absorber tubing of these systems are linked together toheat water and in turn generate steam to drive a turbine generator toprovide electricity. The parabolic concentrators are generally made ofglass with a mirror backing material and include a sturdy framing systemthat is positioned or controlled with a computerized one axis trackingsystem. The parabolic concentrators are generally focused to heat anabsorber tube made of tempered glass and containing water, oil, or thelike that is pumped through the tube (which is generally 5 to 10-inchesin diameter) at the correct rate depending upon the length of theconcentrator and corresponding to the overall size of the system.

While being desirable for using a renewable power source, CST systems,such as those that utilize parabolic concentrators with single-axistracking capabilities, have not been widely adopted. One drawback withCST systems is that they tend to be quite inefficient, and this lack ofefficiency is especially acute during months where the incidence angleof the sun is the furthest from perpendicular. Collecting efficienciesdue to the skewed focus of the troughs can drop to under fifty percentin these conditions. In addition, the absorber tube or pipe carrying theheated fluid may be relatively large in diameter and is located directlyin front of the concentrator (i.e., in the trough of the parabolicreflector or the like), which shadows the overall collection device anddecreases efficiency further. Efficiencies of CST systems are a concernas the overall efficiencies from collector to grid may be as low asabout fifteen percent. Hence, there is a need to enhance efficiencies ateach step of the process including collection and thermal efficienciesproximate or within the collector assembly.

Additional drawbacks of conventional parabolic concentrators includeexpense of manufacturing, lack of efficiency during many months of theyear (e.g., due to non ideal azimuth angles), and fragility of theparabolic trough materials (e.g., which may lead to damage under normaloperating conditions such as due to weather conditions including hail,strong winds, and the like). In addition, parabolic reflectors orconcentrators tend to be quite dangerous to work around during sunlighthours as they produce concentrated beams of sunlight that can causesevere burns and even blindness and as many of the parts of the systemare at very high operating temperatures.

Further, one of the larger drawbacks is the need to maintain thereflector and absorber tubing outer surfaces in a very clean state tomaintain light collection and thermal efficiencies in desired ranges. Asa result, a problem with parabolic concentrators is the difficulty ofcleaning the systems including the large usage of cleaning chemicals andwater. Large systems require constant cleaning and rinsing, adding costsand, over time, contaminating soil underneath the reflectors. In desertconditions where many CST systems are located, it is particularlyexpensive and difficult to provide water for cleaning these units. Mostarrays are cleaned by crews on an ongoing basis or seven days a week,which increases the maintenance or operating costs associated withgeneration of electricity with CST systems.

Hence, there remains a need for a more modern, scalable concentratorsystem. Preferably, such a concentrator system would be easier to cleanincluding using less water and chemicals. The system may be cheaper tomanufacture and less dangerous to operate and maintain (and more durablesuch as being less likely to be damaged by hail or the like). Further,the concentrator system may be more efficient (with a lower cost perwatt of generated electricity). Still further, the concentrator systemmay be useful for heating a variety of transfer or working fluidsincluding heating oil, glycol, air, or other liquids and also have theability to function as a photovoltaic concentrator at the same time orindependently from heating a working or transfer fluid.

SUMMARY OF THE INVENTION

The present invention addresses the above and other problems byproviding a concentrator for a solar energy system (e.g., a concentratedsolar power (CSP) system) such as a scalable, linear Fresnel collectorsystem or assembly that uses fiber optic wafers or pipes. It is believedsuch as a concentrator will cost significantly less than conventionalparabolic trough collectors while providing efficiencies of fiftypercent or, more likely, higher efficiencies.

Concentrators for use with solar technologies, including concentratedsolar power (CSP) systems, are becoming increasingly efficient and arebeing used primarily for concentrating sunlight to create heat forgenerating electricity. CSP systems producing electricity using heat(rather than photovoltaic (PV) surfaces) typically are configured togenerate heat sufficient to create steam, which, in turn, is used todrive a turbine or sterling engine to generate electricity. Mostconcentrators, such as parabolic trough concentrators, provide limitedefficiencies, have high associated manufacturing and maintenance costs,and utilize mirrors rather than lenses to concentrate sunlight. In themajority of these CSP systems, the collector or receiver (or absorbertube) is located in front of the mirrored surfaces of the reflector andcauses shadowing, which leads to decreased efficiencies. High qualitymirrors or reflectors are also very expensive to manufacture and requirea great deal of maintenance (e.g., cleaning) to maintain theirreflectivity. Most of the existing CSP technologies utilize trough ordish technologies, and both of these collector technologies havemarginal efficiencies and present problems for collecting thermal energyfrom the Sun over differing seasons and even during a single day's time.

Traditional trough collectors may have several sunlight or ray “bounces”before the rays hit the linear collector or absorber tube. The troughmay be fixed in place but, more typically, a tracking system or assemblyis provided to move the large trough to better track the changingposition of the Sun and direct a larger percentage of received sunlightonto the linear collector or absorber tube. Generally, trough collectorsuse a single-axis tracking system to modify or adjust orientation of thetrough in the east to west direction (e.g., attempt to follow the Sun'smovement across the sky in daylight hours). Parabolic trough collectorsmay have maximum ray collection efficiencies (which may also be measuredas thermal efficiencies) of about 60 to 80 percent with net efficienciesof about fifty percent or less after reflectivity deductions, shadowingand off azimuth angle averages during the year are fully considered. Afurther concern is that the trough designs often have to be limited to aparticular size and particular concentration ratios.

Due, in part, to these limits associated with parabolic troughcollectors, other collectors have been designed and implemented in CSPsystems but with limited success. For example, dish collectors have beenused in CSP systems. Dish collectors provide two axes of tracking thatprovide an advantage over the single-axis tracking of trough systems asit allows adjustments to be more readily made for seasonal changes inthe Sun's location. However, dish collectors present scaling and otherproblems. The mirrors for the dish-shaped reflector or collector aredifficult to build economically. Also, there is presently not apractical solution for linking more than one unit together such as tofacilitate the creation of steam to run turbines or other powergeneration devices in scale for conventional or thermal storage powerplants.

In other CSP systems, desert towers are used to create a great deal ofheat by using mirrors positioned around a tower to focus toward thetower. Unfortunately, these systems are very expensive to fabricate andmaintain as well as being relatively dangerous to operate. Further,tower-based CSP systems require a great deal of land (e.g., have a largefootprint or land-use profile) and require significant amounts andnearly continuous maintenance to continue to operate near or in designefficiency ranges.

In some cases. Fresnel lenses have shown promise for use inconcentrators. The use of lenses have led to scaling problems, though,as concentration ratios in linear collectors are limited (e.g., 300 to1), and larger lenses (including Fresnel lenses) have extremely longfocal lengths that are difficult to manage or manipulate withconventional tracking as found in parabolic trough collectors. Forexample, some of larger Fresnel lenses may have focal lengths of 40 feetor more and are assembled in pieces. To get the power to one spotlocation, such large Fresnel lenses may have to be mounted high in thesky to focus on a “spot” location, and, in the past, there had been noway to consolidate the heat with adjoining lens arrays. Since parabolictroughs cannot reach ideal temperatures for making steam (e.g., ideally,temperatures in excess of 1000° F.) and towers do not integrate wellinto existing coal or natural gas plants, there has not been an idealconcentrator available within the solar energy industry.

The inventors recognized the need for a new type of collector or“concentrator” that may be used for thermal power generation, in thermalPV systems, and concentrator PV systems. To this end, the inventorspropose a concentrator for a solar energy system (e.g., a concentratedsolar power (CSP) system) such as a scalable, linear Fresnel collectorsystem or assembly that uses fiber optic wafers or pipes. Theconcentrator may be thought of as a tracking, integrated lens andoptical wafer concentrator (or a Fresnel lens-based trackingconcentrator utilizing fiber optic wafers or pipes). The describedconcentrator (and CSP systems including such a concentrator) solveseconomic issues, scalability issues, temperature issues, and otherissues associated with prior solar collector technologies while allowingeasy integration of the concentrator into gas plants and coal plants.

More particularly, a solar power system is provided for supplyingconcentrated solar energy, such as via a working or transfer fluid orvia PV materials or devices, to a power generator or thermal storage.The system includes a collector and a concentrator assembly. Theconcentrator assembly includes an array of two or more linear lenses(such as planar or arched linear Fresnel lenses with a width of 4 to 10inches or more and a length extending along the concentrator). Theconcentrator assembly also includes a set of optical wafers each havinga planar body and each being paired with one of the linear lenses todirect light focused by the corresponding lenses onto the collector.Specifically, a first edge of the body of the optical wafers issupported in the concentrator assembly to be proximate to the array oflinear lenses (e.g., supported by a support plate with a linear edgefacing toward one of the lenses). Additionally, a second edge of thebody of the optical wafers (opposite the first edge) is positionedproximate to the collector, and each of the linear lenses focusesreceived sunlight onto the first edge of the paired one of the opticalwafers. In this manner, a portion of the sunlight focused by each lenson an edge of the optical wafer is transmitted through the opticalwafers to the collector (and out the second edges of the wafers that actas light pipes for the concentrated sunlight or solar energy).

In some embodiments, each of the bodies of the optical wafers is formedfrom a light transmissive material (such as a plastic, glass, orceramic), and the focused sunlight that enters the body at the firstedge is retained within the body using total internal reflection. Thelens array may be spaced apart from the first edges of the bodies of theoptical wafers by a lens array height, and this lens array height isselected based on a configuration of the linear lenses such that a focalpoint for each of the linear lenses is proximate to one of the firstedges along a length of the concentrator assembly (e.g., light for eachlens is focused along a line that coincides with the first edge of apaired/corresponding light, wafer). Significantly, the lens array ispositionable within the concentrator assembly to adjust the lens arrayheight such that the focal points of the linear lenses substantiallycoincide with one of the first edges of the optical wafers to cause thefocused sunlight to enter the optical wafers. For example, theconcentrator assembly may include an array positioning mechanism orassembly adapted to provide two-axis tracking of the lens arrayincluding tracking a position of the Sun during daytime hours andperiodically adjusting the lens array height based on the Sun's azimuthto match a focal length of the linear lenses to the array height.

In some embodiments, each of the linear lenses is substantiallyidentical in configuration and is a linear Fresnel lens. Moreparticularly, the system may have an array of lenses including at leasteight of linear Fresnel lenses (e.g., arched Fresnel lenses with theflat side facing outward to facilitate cleaning). In some cases, thecollector includes an absorber tube or pipe with a light-transmissivesidewall (e.g., glass, plastic, or ceramic material cylindricalsidewall) through which a volume of working fluid flows during operationof the solar power system. Then, the second edge of each of the bodiesof the optical wafer is positioned about a circumference of the sidewallto target the portion of the focused sunlight into the working fluid(e.g., eight to twelve or more planar wafers may be positionedequidistally about the circumference of the absorber tube to target theflowing working fluid from eight differing angles to morereadily/equally heat the working/transfer fluid).

In some embodiments, the concentrator assembly further includes a sleeveextending along the length of the absorber tube and spaced apart adistance from an outer surface of the absorber tube. The sleeve rotatesabout the absorber tube when the position of the lens array is adjustedto track a position of the Sun. The gap may be air filled or filled witha second fluid such as one that has excellent heat transfer qualities topass heat from the shell/sleeve to the absorber tube if the shell/sleeveis a heat conducting material rather than a light transmissive material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a functional schematic view of an embodiment of aconcentrated solar power (CSP) systems of the present invention showingthe combination of an adjustable position (or height) lens array with anarray of optical or light wafers/pipes to concentrate sunlight onto areceiving surface (e.g., PV material or the like with an absorber tubecarrying working/transfer fluid being shown);

FIG. 2 illustrates an end view of another embodiment of a concentratorassembly such as may be used in the CSP system of FIG. 1 or other CSPsystems;

FIG. 3 is a sectional end view of a collector assembly showing itsstar-like appearance due to the positioning of 2 to 12 or more lightpipes or wafers (with 8 shown in this non-limiting example) about acircumference of a collector or absorber tube;

FIG. 4 illustrates a collector assembly in a sectional view showing useof a shell/sleeve to support second/output ends of light wafersproximate to an absorber tube or collector while allowing the shell torotate with tracking in a concentrator assembly;

FIG. 5 shows an embodiment of a light wafer that is a composite designincluding two or more planar sheets of material to create a wafer withincreased width to provide an enlarged or wider light-receiving surfaceat an end or edge of the light wafer;

FIGS. 6 and 7 illustrate ray tracing plots for a portion of concentratorassembly with a fixed array height but light at two differing seasonalSun positions;

FIG. 8 is a plot indicating a fraction of light reflected versusincidence angles in a light wafer illustrating aspects of total internalreflection utilized in the present invention; and

FIG. 9 is a ray tracing of an embodiment of a concentrator assemblyuseful for showing the effectiveness of the light wafers incollecting/receiving focused light and then adjoining the wafers to acollector to concentrate sunlight, e.g., to heat a transfer or workingfluid in an absorber tube.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is generally directed toward new concentrators orcollectors for more effectively collecting solar energy throughout theday and over two or more seasons. FIG. 1 illustrates schematically (orin functional block form) a concentrated solar power (CSP) system 100 ofone embodiment. As shown, the CSP system 100 includes a concentrator orcollector assembly 110 that combines a lens array with a set or array oflight wafers, and the concentrator assembly 110 may be tracking and/orhave the lens array be adjustable to adjust for daily and/or seasonalchanges in the position of the Sun 102.

Briefly, the CSP system 100 includes the concentrator assembly 110 thatincludes a housing 120 in which a lens frame or support 122 is providednear an upper opening. The housing 120 also includes a wafer support orplate 124 that is typically rigidly mounted in the housing 120 andsupports a first or receiving end 144 of a plurality of light wafers orpipes 142 (e.g., a set of focal points or lines are presented on anupper surface of plate 124). Significantly, the concentrator assembly110 also includes a lens array 130 made up of a plurality of linearlenses 134 (e.g., linear Fresnel lenses or the like) each with a width,W_(Lens), and a length, L_(Lens) (e.g., with a length, L_(Lens), that ismuch greater than the width, W_(Lens)). The elongated (and generallyplanar) lenses 134 are supported in the frame 122 with an upper orreceiving surface facing outward from housing 120.

As shown, the concentrator assembly 110 is positioned to receive solarenergy or sunlight from the Sun 102. The lenses 134 of the lens array130 are arranged to focus light 108 onto first ends/edges 144 of anarray 140 of light wafer or pipes 142. To this end, the array 130 may bemoved 123 to change its relative distance or height, H_(Array), from thesupporting plate 124 and receiving or first edges 144 of wafers 142. Insome preferred embodiments, the distance, H_(Array), is chosen and thelenses 134 are configured to focus on the focal point/line coincidingwith the edges 144 of wafers 142. The wafers 142 are typically sheets ofplastic or the like configured to trap and transport, withoutsignificant losses, the light 108 from the first end/edge 144 to thesecond or outlet end/edge 146, which is abutting an a receiver orabsorber tube 150.

The concentrator 110 further includes an array position and trackingassembly 160 that is adapted to alter the position of the lens array 130to track the position of the Sun 102 relative to the light receivingsurface of the lenses 134. For example, the assembly 160 may include acontroller (e.g., an electronic or computer device with a processorrunning one or more sets of code to perform particular functions) 162that selectively issues control signals to a servo motor or similardevice 164 to pivot the array 130 on an axis to provide intradaytracking. Further, the servo motor 164 preferably is able to set andchange 123 the distance or height, H_(Array), above the plate 124 andreceiving edges 144 such that the lenses 134 focus the light 108generally into the wafers 142. The adjustment of the separatingdistance, HArray, between the lenses 134 and the receiving edges 144 isa significant aspect of the invention and is discussed in detail below,and this feature is provided to adjust the array 134 to account forseasonal changes in the position of the Sun 102 (e.g., the angle ofreceived sunlight 104 that changes over the course of a year). Theoperation of the controller 162 may include running one or more trackingprograms 166 that may define height, H_(Array), such as based on acalendar and geographical location of the concentrator 110, and that mayprovide input for daily tracking operations for concentrator 110.

The light 108 then travels within the wafers 142 to be output atends/edges 146 into the tube 150. A working or transfer fluid 113 is fedinto the tube 150 at an inlet 112 to the concentrator 110 at a first,lower temperature, T_(In). Along the length of the absorber tube 150between the inlet 112 and outlet 114, the fluid is heated byfocused/concentrated (and combined) light 108 so that the fluid 115 isoutput at the outlet 114 at a second, much higher temperate, T_(Out).The tube 150 may be formed with substantially transparent sidewalls (ofglass, plastic, or ceramic materials) and support the ends 146 to directthe light 108 through the sidewalk. The heated fluid 115 may then betransferred to a power generator or thermal storage 116 where thecollected solar energy may be utilized such as by creating steam todrive a conventional steam generator, to heat materials for thermalstorage, and so on as is well known in the power industry. Oneconcentrator 110 is shown in CSP system 100 but, of course, a typicalCPS system 100 will include a much larger number of such concentrators110 providing a system or field of solar piping 114 that would becombined at inlet and outlet manifolds to the power generator/thermalstorage 116.

In one embodiment, the lenses 134 are linear Fresnel lenses. Such linearFresnel lenses 134 may be curved or flat and made of a variety oftransparent materials (or at least translucent to substantiallytransparent materials) such as a glass, a plastic, a ceramic, or acombination thereof. Linear Fresnel lenses 134 may be extruded at highrates of speed and may be up to 8 feet or more wide, W_(Lens), andnearly infinitely long, L_(Lens), (with 20 to 50 feet or more in lengthbeing common for many arrays 130). The lenses 134 are assembled inframe(s) 122 and mounted next to each other (width wise) to provide eacharray 130. Several lenses 134 may be mounted across the frame 122 toprovide an array 130 having a width of 50 feet or more. Focal lengths ofthe lenses are usually around 1.5 times their width, W_(Lens), but thismay vary depending upon the lens design. In some cases of concentrator110, therefore, the height, H_(Array), may be adjusted 123 by arrayposition assembly 160 to be about 1.5 times the width, W_(Lens). Thedesign of the arrays 130 allows the collecting unit 110 to remain lowprofile, yet provide very large concentration ratios.

Linear Fresnel lenses can be made from extrusion, casting into thepolymer, or applying ultraviolet (UV) beams or E-Beam (energy curedpolymers) over a sheet or roll of material (e.g., a plastic). Forcommercial and industrial concentrators, the width of the lenses wouldnormally be selected from a range of about 8 inches to about 8 feet ormore. Most industrial extrusion lines have widths of about 4 feet wideat their maximum; however, there are extrusion lines (and devices) thatare over 8 feet wide such that these or other practical limitations mayset the lens width of the lenses in each lens array. The Fresnel lensescan be made from thicknesses of about 0.03125 inches to about 0.25inches or more depending upon the application. In some cases, theFresnel lenses can be made in sections and pieced together in both (oreither) length and width, forming widths of over 4 meters and nearly anydesired lengths.

Fresnel lenses for the lens arrays of the concentrators can be made, insome exemplary processes, at a rate of over 20 feet per minute in,extrusion and over 100 feet per minute in energy cured casting. As aresult, it will be appreciated that the production of the Fresnel lensesmay be very fast and is readily scalable. Materials of choice for theFresnel lenses include, but are not limited to PMMA (or poly(methylmethacrylate)), acrylic, fluoropolymer, polycarbonate, and glass.Selection of the width of the lenses corresponds in most cases to thefocal length of the lenses (and desired distance to thereceiving/leading edge of the light wafers of thecollector/concentrator), and, therefore, in an industrial concentratorthe height of the overall device. Generally speaking, to reduce Fresnelreflections, focal lengths are normally about one to two times the widthof the Fresnel lens.

Fresnel lenses used for these concentrators can be curved Fresnel lensesor flat Fresnel lenses. Typically, the lenses for these concentratorsare positioned within the lens array and supporting frame with thestructures of the Fresnel lens facing down or away from the Sun (e.g.,FIG. 1 shows, for ease of illustration, the curved and structured partof the lenses 134 up but this arrangement may be reversed in someembodiments of the concentrator 110). The Fresnel lenses made with thestructures down provide a smooth top, which makes the lenses easier toclean, whether they are flat Fresnel lenses or curved Fresnel lenses.

The decision as to whether use curved Fresnel lenses or a flat Fresnellenses may be based upon the application, costs, and other factors. Anadvantage to using curved Fresnel lenses versus flat Fresnel is theirability to more readily focus larger angles of incidence making them amore forgiving lens for focusing. The facets in the Fresnel lenses canbe made in various sizes, from as little as 1/1000-inch to over ⅛-inchwith from about 1,000 facets per inch to less than 6. On the average, anextruded lens will have between 50 and 500 facets per inch, and mostenergy-cured lenses will be much finer, e.g., utilizing between 100 andabout 1,000 facets per inch. Normally, energy-cured lenses are made onthinner films, and they may then be laminated to thicker PMMA oracrylics for structural integrity.

For the concentrators described herein such as concentrator 110,multiple lenses 134 are lined up in a frame 122, and their energy 108 isjoined together by light wafers 142. This allows the Fresnel lens array130 to have a low profile (smaller width, W_(Lens), and, therefore,shorter focal lengths (i.e., H_(Array) in preferred arrangements ofconcentrator 110) creating a lower profile) yet combine their energytogether for a higher concentration ratio.

In some cases, the light wafers 142 are sheets of glass or plastic(e.g., one preferred material is low-iron glass) of various thicknessesand sizes. The wafers behave much like commonly used fiber optic cable.Light enters through the edge 144 and bounces around the inside of thelight wafer (or its planar body), which results in loss of very littleenergy and the received/focused light 108 from lenses 134 exits out theother end. As shown in FIG. 1, each lens 134 may be paired with at one(or more in some embodiments) light wafer 142 (e.g., be focused onto oneedge 144). The glass or plastic can be bent to aim its end or edge 146at a target, which in this case is a cylinder or tube 150 (while someembodiments may target a flat collector such as a collector or receiverwith PV material or the like). Bends in the wafers 142 (e.g., in thesheets of glass or plastic) preferably are gradual so as to prevent therays from leaking or escaping (or limiting such losses) by providinglight ray bounces that exceed +/−21 degrees. In some embodiments, thelight wafers 142 may be made of float glass, and then bent to theengineered shape with heat, or the wafers may be poured directly intothe mold needed.

The Fresnel lens array 130 focuses light 108 down into the first orreceiving ends of the light wafers 144, which are supported in plate ortray 124. The focused or concentrated light 108 then travel through thewafers 142 to the collector hub and cylinder collector 150 (exits secondor outlet end 146 of each wafer 142). In other words, the lenses 134focus into the side 144 of the glass or plastic sheets 142 and light 108travels through the “wafer” using total internal reflection (TIR)entering the wafer and remaining within the limits of TIR (e.g., about+/−21 degrees). The glass or plastic wafer may be from less than 1/32″to over several inches thick.

The incoming rays 108 must remain parallel to the entrant point at theside 144 of the glass or plastic (or other material) wafer 142 withinthe necessary +/−21 degrees parallel with the wafer sides, even in thebends of the glass, plastic, or ceramic wafer 142. Since the rays 108travel through the glass, plastic, or ceramic wafers 142, it ispreferred that care is taken in the design/installation of wafers 142 tonot bend the wafers 142 radically so as to successfully contain/retainthe rays 108 in the wafers 142 between ends/edges/sides 144, 146.Briefly, each of the wafers 142 is configured or bent gradually toprovide a light path for light 108 from a particular one of the lenses134 toward the collector 150 and its contained working fluid 113, 115.

Since very little energy is lost after the rays 108 enter the wafers 142(dependent upon the purity of the materials used for the wafers 142),the rays 108 move through the wafers 142 at high efficiencies. The netray collection count in a concentrator assembly 110 of the presentinvention will likely be in the range of about 90 percent to about 100percent. The net efficiencies with the surface interface lossesconsidered will likely be up to about 80 percent to about 85 percent.General losses occur as Fresnel losses at the bends of the wafers 142,and 5 percent coming into the wafers 142 at edge 144 and back out of thewafers 142 at edge 146. However, despite these losses, the Fresnellens/wafer combination concentrator 110 exceeds the efficiency of mostother concentrators and is less expensive to manufacture.

The CSP system 100 may use the concentrator assembly 110 to heat a widevariety working/transfer fluids. For example, the fluid 113, 115 may bea glycol, water, nearly any liquid material, and a gas such as air toprovide solar energy with heated fluid 115 to the powergenerator/thermal storage 116 (i.e., any device that may utilize energyin fluid 115). In other embodiments, not shown but part of thisdescription, the concentrator 110 may be configured for use as a PVconcentrator or a combination of PV and thermal concentrator such as byreplacing all or portions of the absorber tube 150 with PV devices suchas solar cells or panels or the like.

As shown in FIG. 1, the CSP system 100 may fill the collector orabsorber tube 150 with glycol, oil, liquid salt, or any number ofliquids/solutions. In one case, the CSP system 100 is configured as awaterless, high-efficiency thermal system. Particularly, the collectorsystem with absorber tube 150 may be a closed loop system with the oilor other transfer fluid 115 filling the collector pipe 150 and beingcirculated (via pumps or the like not shown) into a coil in a salt tankin the power generator/thermal storage 116. The salt is heated by thefluid 115 and, in turn, heats a hydrogen unit for a heat exchangerdriving a Sterling engine (e.g., closed-loop hydrogen process). In othercases, the collector 150 may be configured to wrap around a heating unitin the generator/storage 116 to directly heat the hydrogen (or othermaterial) driving a Sterling engine and heat exchanger. Part of theenergy 108 may be collected concurrently (or in place of fluid 115) insome of wafers or the like in a PV application.

The CSP system 100 may be operated as a one-axis system without trackingas to seasons. However, such a system 100 would have some issues ornuances. The one-axis system 100 would be configured with arrayposition/tracking assembly 160 to track much like a Sun trough, e.g.,running north and south in length and tilting east in the morning andtracking the Sun directly overhead to west in the evening. The mainissue is the seasonal azimuth of the Sun. Changes in seasonal azimuth ingeneral prohibit perfectly aligned rays from being properly directedinto the sides 141 of the wafers 142. Much of this is a result of thefocal length changes in the linear lenses 134 being either two long ortoo short, therefore missing the edge 144 of the wafers 142 slightly.

Two factors may be used in implementations of the present invention toovercome this problem almost completely. First, the wafers 142 can bemade slightly wider than would be needed should a perfect focus beachieved. In other words, the first or receiving edge/end 144 would thenbe large enough that in mid-summer the rays 108 would be centered in itswidth while in other seasons the rays 108 (or most of the rays 108)would still be within the boundaries of the edge 144 (i.e., the focalpoint/line of the lenses 134 would generally coincide with the positionand width of the edges 144). Second, the lenses 134 may have a secondmodified “axis” by configuring the concentrator assembly 110 to have theability (via array position/tracking assembly 160) to raise slightly orlower slightly (123) with the azimuth of the Sun 102, thereby adjustingthe focal lengths of the lenses 134 slightly to accommodate the seasonalazimuth helping to eliminate over and under focus (e.g., vary the arrayheight, H_(Array), a small amount over the year to account for seasonalmovement of the Sun 102).

Such an arrangement and operation of the is explained in further detailwith reference to FIG. 2, which shows an end view of a concentratorassembly 210 with a tray 222A and 222B holding lenses 234 of a lensarray 230 in an up or summer position (shown at 222A) and in alowered/down or winter position (shown at 222B). A drawback of mostparabolic trough concentrators is that as the seasonal azimuth changesthe focal length of the rays and the concentration efficiency greatlydiminishes as many of the rays do not hit the collector properly.Whereas complete 2-axis adjustments provide accurate focus, it isimpossible to take lengthy arrays and turn them on their side andaccomplish 2-axis tracking in a conventional parabolic troughconcentrator.

In contrast, though, the concentrator assembly 210 includes a lens array230 of lenses 234 (e.g., an array or number of linear Fresnel lenses). Aservo 260 (or similar vertical positioning device) may be used to move261 the lens array 230 (or the lenses 234 on support tray up 222A anddown 222B to adjust for the shortening of the focal length in the winteror when the normal incident angle of the Sun relative to the positioningof the concentrator assembly 210 provides angles other than perfectlyperpendicular. By having the ability to lower or raise 261 just the lensportion 222A and 222B to lenses 234 can be positioned to receivedsunlight 204 and properly focus the light 208 onto or so as to meetreceiving surfaces 245 on the first/receiving ends/edges 244 of lightwaters 242 as the focal length decreases or increases.

The height, H_(Array), of the lens array 230 is measured from the lenses234 (or their back or inward facing surface) to the receiving surfaces245 of the first ends 244 of the wafers 242, and the servo 260 is drivento move the tray 222A, 222B through a relatively small adjustment range(or adjustment height, H_(Adjustment)) so as to properly account forchanges in the Sun's azimuth. Such adjustments may be performedperiodically such as weekly or even daily to maintain the focusing oflight 208 onto the receiving surface 245 of wafers 242. The ends 244 mayprotrude outward some distance from a support plate 224 attached tohousing 220 or may be flush as shown in system 100.

Such operation of the servo or vertical positioning device 260 allowsthe concentrator assembly 210 to be much more efficient than aconventional trough concentrator. In addition, this movement 261 doesnot affect the stationary positioning of the collector itself or of thelight wafers 242, which remain attached at their second or outlet ends246 to the sides of the stationary collector or absorber tube 250 (e.g.,remain targeted onto a desired collector surface which may be PVmaterials or devices or sides of a fluid containing tube). While thewhole unit (e.g., frame 220 containing the collector 250, wafers 242,wafer support plate 224, and lens array 230) rocks back and forth fromsunrise to sunset in a one axis system, the servo 260 operates inassembly 210 to continue to adjust 261 the lenses 234 slightly up anddown through a height adjustment, H_(Adjustment)) using servos or othermeans of mechanical adjustment 260 for the time of season to adjust forthe season and the corresponding Sun's seasonal arc.

The concentrator assemblies described herein may be thought of asincluding a “star” collector because of its sectional or end view asshown in FIG. 3 with collector assembly 300. As shown, the collectorassembly 300 includes a collector or absorber tube 310 with acylindrical sidewall 312 having an outer surface 314 and an innersurface 316, which defines an inner volume or space through which thetransfer or working fluid 320 is caused to flow during use of thecollector 300. The star collector 300 further includes a light waferarray 330 that includes a number (8 are shown but up to 12 or more couldreadily be used to suit a lens array, a circumference of tube 310, orthe like) of light wafers or planar light pipes 332.

Each wafer 332 extends from a first or receiving end (not shown) thatreceives light focused from a linear lens of a lens array to a second oroutput end 336. The second end 336 is positioned flush against the outersurface 314 of collector sidewall 312 or is targeted to direct the light333 onto such surface 314. The light 333 is retained via TIR withinwafer 332 as it strikes and bounces off of inner surfaces 334, 335 ofplanar wafer 332. In some cases, the number of wafers 332 is chosen incombination to the outer diameter of the collector/tube 310 such thatall, or nearly all, of the outer surface 314 is covered with edges/ends336 of wafers 332 in wafer array 330.

The star collector 300 is unique as it allows incoming energy 333 fromthe light wafers 332 to strike the collector 310 from all (or many)angles about its circumference rather than from a single direction as isthe case with parabolic trough collectors. In other words, the starcollector 300 is a 360-degree collector. The light 333 can exit the end336 of the wafer 332 and directly strike the cylinder's sidewall 312 onits outer surface 314.

However, since the wafers may be moved during daytime and seasonaltracking movements, it may be useful in some embodiments to have aslight space between the end of the light wafer and the cylinder orabsorber tube. FIG. 4 illustrates such a collector assembly 400 thatincludes a stationary or fixed absorber tube or collector 410. Thecollector 410 includes a cylindrical sidewall 412 with an outer surface414 and an inner surface 416 defining an inner space or volume throughwhich fluid 420 flows during use of collector assembly 400. Thecollector assembly 400 further includes a wafer array 430 with aplurality (e.g., 4 to 12 or the like) of planar light wafers 432 withinner surfaces 434, 435 that trap light 433 from a corresponding lens(not shown) and discharge all or much of the light 433 out a second oroutput end 436.

The collector assembly 400 allows movement of the ends 436 of the wafers432 by providing a cylindrical shell 410 with a sidewall 472 having anouter surface 474 and an inner surface 476 proximate to but spaced apartfrom the outer surface 414 of the absorber sidewall 412. As a result, aspace or void 478 is defined between the shell 470 and the absorber tube410 such that the shell 470 may rotate 473 about the outer surface 414.In some cases, a servo motor (not shown) may rotate 473 the shell 470 toaccount for tracking movements of the concentrator assembly containingthe collector assembly 400 or the shell 470 may simply move with theends 436 of the wafers 432, which may be rigidly attached (withtransparent adhesive or the like) with outer surface 474 of shellsidewall 472. The gap or space 478 is defined by the values of the innerdiameter, ID_(sleeve), of the sleeve or shell 470 and the outerdiameter, OD_(Tube), of the absorber tube 410 (which is smaller tocreate a rotation-facilitating space between the stationary and rotating473 components).

In this manner, the wafers 432 and shell 470 have the ability to rotate473 around the collector 410 holding the liquid, air, or solid 420 yettransmit the heat 433 to the collector 410. In some cases, the sleeve470 might also be wrapped in a PV material (facing outward on outersurface 474). The sleeve sidewall 472 may be formed of a translucent orlight transmissive material to transmit the light 433 onto the absorber410. In other embodiments, though, the sidewall 472 may be made of aheat conductive material such that it heats up and then transfers heatto collector 410 and working fluid 420, e.g., so that the interior 416of the collector 410 and its contents 420 heat up and hold heat unitdispersed or used in energy production. In such latter embodiments, thespace or gap 478 may be filled with a heat transfer fluid thatfacilitates more rapid heat transfer (relative to air) while allowingready rotation 478 of the shell 470 about the tube 410. In eitherembodiment, it may be desirable to minimize the size of the gap 478 tocontrol inefficiencies of heat transfer or loss of energy between shell470 and tube 410.

As will be understood, a concentrator assembly that combines theabove-described features (i.e., a sleeve 470, wider than needed lightchannels/wafer thickness (or multiple sheets or wafers combined as shownbelow) that give the rays a larger “target” into the side of the wafersand help to capture the rays, and the ability to raise and lower thelens array to adjust their height or separation from the ends/edges ofthe light wafers) allows a “game changing” amount of heat to be drivento the collector. The inventors believe CSP systems with one or more ofthese concentrator assemblies represent a disruptive technology becauseof low cost to manufacture, low cost of maintenance, and extremely highheats obtained at the collector (and in its working/transfer fluid or onPV materials/devices). For example, a linear device CSP system will beable to safely and inexpensively provide a temperature in excess of1,000° C. for vast amounts of fluids. The volume of liquid/fluid heatedand the temperatures of that liquid will be able to far exceed thermaltowers, parabolic troughs, and other devices. Another large advantage ofthe device is that the plumbing for the device (e.g., the absorber tube)can remain stationary while the wafers and other portions of theconcentrator assembly pivot around the absorber tube or heat-receivingcollector components. Hundreds or even thousands of feet of absorbertubing may be integrated into a solar field pipeline achieving a largeamount of cumulative solar energy in a CPS system (with the shell beingheated and heating the absorber tubing or transmitting the light/energythrough to the absorber tubing so as to effectively heat the transferfluid).

The collector assembly can be very long each linear lens along with anassociated planar light wafer and absorber tube and two or morecollector assemblies of a CSP system may be linked together in “rows” ofcollectors. As a result, a larger volume of working fluid may be heatedwith this device than with a conventional trough device. The CSP systemwill likely have much greater heat delivery, with a fraction of the perfoot cost and with less maintenance when compared to a CSP system usingparabolic troughs.

For instance, a 50-foot wide collector (measured across a width of aplurality of lenses in a lens array) may have a concentration ratio of:CR=W/SA×EFF of collector, with CR=Concentration Ratio; W=Width ofdevice; SA=Surface Area of collector; and EFF=Efficiency. Further, acollector assembly may utilize a cylindrical absorber tube that wouldhave a surface area determined by the equation SA=Diameter of Tube×Pi.Hence, a 50-foot wide collector with a 2-inch diameter collection pipeat 80 percent efficiency would deliver the following:50(12)/2(314)×0.80=600/6.28(0.85)=95.54 CR (i.e., a concentration ratioof 95.54)

An impressive part aspect of the described concentrator assembly is thatit is a continuous and not a spot collection system. In addition, it isthree to ten times more powerful than most trough collector systems.This can equate to more than one thousand degrees Celsius of continuousheat. Therefore, at sea level, a 50-foot wide by 1000-feet longconcentrator assembly would be able to deliver 1,184.513 kilowatts (KW)based on the following: (1) 15.24 meters×304.80 meters=4,645.15 squaremeters; and (2) (4,645.15) (1,000 watts at sea level) (efficiency of0.85) (efficiency of conversion device of 0.30 for a sterling engine) or(4645.15)(1,000)(85)(0.30)=1,184,513.25 watts or 1,184.513 KW. Thisefficiency makes the collection system extremely efficient while stillbeing inexpensive to manufacture.

In some embodiments of a CSP system, the tops of the lenses (which maybe flat or curved) may be maintained in a relatively clean condition byincluding a washing system. The automatic washing system may beconfigured and positioned relative to the lens array of eachconcentrator assembly to spray and/or wipe the light receiving surfaceor outer surface of the linear lenses (e.g., spray and then wipe with acar-wash like device lengthwise) at regular intervals (e.g., daily,weekly, or the like). Even without regular cleaning, though, the lensarrays described herein are far more forgiving than the level ofcleanliness needed for traditional mirrored parabolic concentrators.

In summary, it may be useful to restate the general parts for acollector assembly of the some embodiments of the invention.Particularly, the parts of a collector assembly with a design with 8lenses that are each 6-inch wide lenses (i.e., an array that is about48-inches across or wide and any useful length long) may include: (1) 8identical lenses (e.g., linear Fresnel lenses of like construction); (2)a center top wafer extending from straight down from a support plate ortray toward the absorber tube (or another type of collector); (3) acenter bottom wafer extending about the absorber tube and arranged todirect light upward into the absorber tube; (4) two sets of identicalside wafers (3 each) bent or curved gradually from the support plateinto the opposite sides of the absorber tube; (5) a frame supporting thelenses of the lens array (e.g., a sealed frame or housing with a bladderand servos for raising and lowering the lenses to adjust the height ofthe array with seasonal changes in the Sun's position to direct or focuslight passing through each lens onto an edge/side of a light wafer); and(6) a cylindrical, flat, or other collector (e.g., an absorber tubethrough which a transfer or working fluid is caused to flow). Aninteresting aspect is that there are very few parts to the concentratorassembly, which facilitates its simple and inexpensive manufacture,assembly, and maintenance.

FIG. 5 illustrates a portion of a collector assembly 510 that includeslarger wafer edges or ends to reduce losses of focused light. Asdiscussed above, it may be desirable to increase the receiving surfaceupon which linear lenses need to be focused to reduce the accuracy atwhich the Sun has to be tracked during the day and/or over seasons. Tothis end, it may not be practical or cost effective to provide a verythick light wafer with a unitary design. Instead, the assembly 510includes a support plate 124 (as shown in the CSP system 100 of FIG. 1)that is used to support the first or light receiving end/edge 542 of alight wafer 540.

The light wafer 540 is fabricated from two or more planar sheets withfour sheets 550, 552, 554, 556 being shown in FIG. 5. The sheets 550,552, 554, 556 may be placed to contact each other at mating surfaces orjoints 560, and affixed to each other to form wafer 540 such as throughthe use of an adhesive or other fabrication methods (e.g., EVA or thelike). In this manner, the end 542 provides a light receiving surface544 that has a width, W_(Wafer), that is four times larger than a singlesheet 550, 552, 554, 556 and increases the likelihood that focused lightfrom a linear lens paired with the wafer 540 can positioned and orientedto have its focal point (or line) on the surface 544.

At this point, it may be useful to again stress how the use of linearlenses such as linear Fresnel lenses arranged in a planar array that canbe moved with a 2-axis tracking/positioning system facilitates thatchanging of the focal point(s) of each concentrator assembly of a CSPsystem to suit seasonal locations of the Sun (and, in some cases, tofirst calibrate an installed assembly after fabrication/shipping). Asthe altitude of the Sun changes during the seasons, a one-axis trackingsystem that relies on lenses or mirrors that focus the light of the Sunon a receiver will not optimally concentrate the light on the receiverfor the various angles of elevation. Such an issued can be seen througha quick review of FIGS. 6 and 7. FIG. 6 illustrates a portion of aconcentrator assembly 600 during use to receive light 630 with one ormore linear lenses 620 and focus light 640 onto a focal point 644. InFIG. 6, the height of the array, H_(Array), is correct for the positionof the Sun providing light 630 to have the focal point 644 coincide withthe collector surface 610 and any edges/ends of light wafers that may becollocated on such surface 610. However, in FIG. 7 the same lens/surfaceseparation, H_(Array), results in the focal point 644 being spaced apartfrom the collector surface 610 (i.e., the Sun's seasonal position hascaused the lens 620 to lose its focus onto the surface 610).

The cause of the change between operation of assembly 600 in FIGS. 6 and7 may be because the path lengths after refraction or reflection changewith the Sun's altitude angle and because only one-axis is presentlybeing used in assembly 600 (day tracking). Hence, the plot of FIG. 6shows the incoming rays 630 and spot patterns 611 at 27 degrees from thevertical along the axis of a cylindrical linear lens are compared to theincident rays at zero degrees incidence, and the assembly 600 in FIG. 6achieves reasonable good focus onto the collector surface. However, theplot of FIG. 7 shows operation of the assembly 600 at a differing Sunposition, and the incident rays are 27 degrees from the vertical in adirection perpendicular to the plane of the plot. Proper focus is notachieved as the focal point 644 is now spaced apart or is not coincidentwith collector surface 610. Spot diagrams of an array of linear lensesfocusing on a cylinder collector 610 also indicate good focusing alongthe length of the cylinder (along the length of the linear lenses of alens array) in the arrangement of FIG. 6. However, spot diagrams of thesituation shown in FIG. 7 show that there is a spread of rays along aY-axis (e.g., focal point 644 is not on the cylinder's surface), whichis detrimental as some of the rays 640 will miss the collector 610 (andnot be available to heat a transfer fluid (or strike PV material)). Theinvention described herein, though, addresses this problem by moving thelens array and its lenses (e.g., arched, linear Fresnel lenses) to anoptimal position or distance, H_(Array), from the collector surface tosuit the Sun's seasonal position to capture the maximum amount of lightpossible.

In order to contain the maximum number of rays possible in the wafers ofa concentrator assembly (such as those shown in FIGS. 1 and 2 (and starcollector in FIG. 3)), some considerations about total internalreflection (TIR) should to be taken into account. As will be understoodby those skilled in the art, there is a dependence of the intensity ofrays as a function of the angle of incidence when in a medium of higherrefractive index than the surrounding medium. For example, FIG. 8provides a plot 800 that was created to compare a fraction of reflection(Y-axis) to the angles of incidence of light (X-axis) within a material(such as a light wafer), e.g., for a material with an index ofrefraction of 1.51 when the surrounding index is 1.00 (air). The plot800 includes lines indicative of average reflection 810, light polarizedparallel to plane 820, and light polarized perpendicular to plane 830 toillustrate Fresnel reflections to illustrate total internal reflection(TIR). The plot 800 shows that when the angle of incidence is around 42degrees, most of the energy of the ray is reflected (via TIR) or trappedwithin the material. Hence, for the planar optical wafers describedherein, as long as the angle of incidence is greater than the criticalangle, rays in the wafers will be contained in the wafer and directed onto the second or output end/edge of the wafer to be targeted onto thecollector (or a shell rotating about an absorber tube in someembodiments).

Hence, in designing a collector assembly in order to meet the aboverequirement to get TIR, the angles of the rays traveling through thewafer need to be taken into account. If the angles are too steep therays will leak out of the wafers before they reach the second end of thewafer and the collector. For example, this can happen in the curvedregions of the wafer where between points of rays striking the wall thecurvature of the wafer has caused the rays to intersect at a steeperangle than the critical angle. To help control such loss, the collectinglenses (e.g., linear Fresnel lenses) preferably are selected to not beof too low of an F number. In Fresnel embodiments, all the rays fromeach Fresnel lens can be designed to enter the corresponding wafer, butrays at large angles of incidence will be the angles of low incidence inthe walls of the wafers. This happens because there is a 90 degree angleof change from the flat surface at wafer entry to the flat side wall forrays entering the wafer. The extreme rays will be the rays to be firstaffected by curvatures in the wafers.

FIG. 9 provides a ray tracing plot 900 created by the inventors as oneproof of concept for a concentrator assembly 915 including a lens array920, a set of light wafers 930, and a collector 950 (in the form of anabsorber tube) carrying a transfer or working fluid 952. The lens array920 includes five lenses 922 that are spaced apart from a receiving orfirst end 934 of the light wafers 932 by a predefined distance,H_(Array), which is chosen such that a focal point 929 of the lens 922coincides with the edge/end 934 of the light wafer 932. Sunlight 910strikes a first surface 924 of the lens 922 and transmitted out from asecond surface 926 as focused light 928. The focused light 928 entersthe light wafer 932 at end/edge 934 where most of the light is trapped933 via TIR and travels along the light wafer to the second end/edge 934that targets a portion of the circumference of collector 950 (so as toprovide the concentrated energy from light 910 to the fluid 952). Somelight 935, though, is lost such as at edge 934 or bends in wafer 932.

The ray tracing plot 900 was generated using a number of assumptions orinput parameters. For example, the lenses 922 were each identical linearFresnel lens that were arched with the facet side 926 facing inward ortoward the optical wafer array 930 and the flat or dome side facingoutward or toward the Sun or source of light 910. The lens 922 had awidth of 8 (such as 8 inches or some other unit of measure may be used),a thickness of 0.2, a pitch of 0.3, and an index of refraction of 1.491.Also, it was assumed that the ray collection fraction was 0.94, theintensity fraction of the rays collected was 0.96, and the netefficiency was 0.90. With the light wafers 932 arranged as shown (withthe end 934 substantially coinciding and aligned with the focal point929 of the lens 922), the temperature at the collector was determined tobe 956° C. or nearly 1000° C.

The thickness of the sheets used for the wafers may vary to practice theinvention. For example, a thickness in practice ranging from about 0.015inches to about 3 inches in thickness may be useful for the opticalwafers, which may take the form of bent sheets of low iron glass or thelike. In some cases, several sheets may be bonded together (e.g., two tofour or more sheets of ⅛-inch or other thickness glass, plastic,ceramic, or other material may be used). The adjoining wafers may beglued together with a polymer or epoxy, may be melted together, orjoined in any way with materials that have a similar refractive index ofthe material used in the wafer material (e.g., glass, plastic, or thelike). Generally, this refractive index will be between about 1.38 andabout 1.95 (or average between about 1.5 and 1.6 which is the range forglass, plastic, or PMMA).

In the tracing, 5 lenses 922 are shown in array 920 but additionallenses may be included in the concentrator assembly 915 (such as 5 moredirecting light into the “right” side of the collector 950 with onedirecting light upward into the collector 950 similar to the arrangedshown in FIG. 4). Alternatively or in addition, the collector 950, aswell as the other collectors/absorber tubes, may have mirrors ormirrored surfaces at locations or positions where edges or ends 934 oflight wafers 932 are not provided so as to reflect back energy or light933 that is not absorbed in the fluid 950. Such mirrors or mirroredsurfaces may be internal to the tube 950 (e.g., mirrors affixed tointernal surfaces of tube opposite the edges 934 of wafers 932), beunitary construction of the sidewalls of the tube 950, and/or be aseparate piece(s) external to the collector/tube 950 (e.g., archedmirrors about the periphery or circumference of the collector 950opposite edges 934 of wafers 932). Mirrored surfaces/elements may alsobe positioned on the surface of collectors between adjacent ones of thewafers (such as in the “star” configurations of collectors shown inFIGS. 3 and 4) so as to better capture all light in a transfer/workingfluid of a collector.

The inventors created and utilized a number of ray tracing programs tofacilitate their design of the collector assemblies described herein aswell as using such programs as a proof of concept. To facilitate othersskilled in the art in achieving the desirable results obtained by theinventors, the inventors are providing portions of the ray tracingroutine source codes for a linear Fresnel lens-based embodiment. Mainly,the Fresnel lenses are designed automatically by the code using theindex of refraction of the lens material as well desired focal lengthsand the widths of lenses as input to the code. The light wafers are thendrawn on the computer screen and adjusted in orientation(curvature/bending) by a designer to eliminate loss of rays at thegreatest curvatures. Collection efficiencies and estimated temperaturesare also calculated by the code. It will be seen by a study of the codethat the code is, in part, a non-sequential ray trace program, e.g., therays are followed wherever the geometry takes them.

As an example, the routine that finds the intersection of a ray with thewafer walls is given:

1. A solar power system for supplying concentrated solar energy,comprising: a collector; and a concentrator assembly comprising an arrayof two or more linear lenses and a set of optical wafers each having aplanar body and each being paired with one of the linear lenses, whereina first edge of the body of the optical wafers is supported in theconcentrator assembly to be proximate to the array of linear lenses,wherein a second edge of the body of the optical wafers opposite thefirst edge is positioned proximate to the collector, wherein each of thelinear lenses focuses received sunlight onto the first edge of thepaired one of the optical wafers, whereby at least a portion of thefocused sunlight is transmitted through the optical wafers to thecollector via the second edges, wherein the collector comprises anabsorber tube with a light-transmissive sidewall through which a volumeof working fluid flows during operation of the solar power system,wherein the second edge of each of the bodies of the optical wafer ispositioned about a circumference of the sidewall to target the portionof the focused sunlight into the working fluid, and wherein theconcentrator assembly further comprises a sleeve extending along thelength of the absorber tube and spaced apart a distance from an outersurface of the absorber tube, whereby the sleeve rotates about theabsorber tube when the position of the lens array is adjusted to track aposition of the Sun.
 2. The system of claim 1, wherein each of thebodies of the optical wafers is formed from a light transmissivematerial and wherein the portion of the focused sunlight enters the bodyat the first edge to be retained using total internal reflection.
 3. Thesystem of claim 1, wherein the lens array is spaced apart from the firstedges of the bodies of the optical wafers a lens array height andwherein the lens array height is selected based on configuration of thelinear lenses such that a focal point for each of the linear lenses isproximate to one of the first edges along a length of the concentratorassembly.
 4. The system of claim 3, wherein the lens array ispositionable within the concentrator assembly to adjust the lens arrayheight such that the focal points of the linear lenses substantiallycoincide with one of the first edges of the optical wafers to cause thefocused sunlight to enter the optical wafers.
 5. The system of claim 4,wherein the concentrator assembly includes an array positioningmechanism providing two-axis tracking of the lens array includingtracking a position of the Sun during daytime hours and periodicallyadjusting the lens array height based on the Sun's azimuth to match afocal length of the linear lenses to the array height.
 6. The system ofclaim 1, wherein each of the linear lenses is a linear Fresnel lens. 7.The system of claim 6, wherein the array of lenses includes at leasteight of the linear Fresnel lenses.
 8. The system of claim 1, whereinthe lens array includes at least eight of the linear lenses and the setof optical wafers includes at least eight of the optical wafers andfurther wherein the second edges of the optical wafers are equidistallyspaced about circumference of the sidewall of the absorber tube.
 9. Aconcentrated solar power system, comprising: an absorber tube; a workingfluid contained within the absorber tube; a housing through which theabsorber tube extends; a support plate positioned in the housing abovethe absorber tube; a plurality of spaced-apart, planar optical waferswith a first end supported by the support plate and a second endpositioned proximate to an outer surface of the absorber tube; and alens array including a plurality of linear Fresnel lenses positionedside-by-side with longitudinal axes in a parallel arrangement, whereinthe second ends of the optical wafers are arranged to be substantiallyparallel to the longitudinal axis of the absorber tube and are spacedapart about substantially the entire circumference of the absorber tube,wherein the system further comprises a vertical positioning assemblyoperating to reposition the lens array to increase or decrease the lensarray height, the operation occurring periodically to adjust forseasonal changes in the Sun's position that cause changes in the focalpoint for the linear Fresnel lenses for the received sunlight, andwherein the system further comprises a sleeve supporting the second endsof the optical fibers in a spaced apart relationship to an outer surfaceof the absorber tube, whereby the sleeve and second ends moves relativeto the outer surface with movement of the lens array.
 10. The system ofclaim 9, wherein each of the linear Fresnel lenses is spaced apart alens array height from one of the first ends of the optical wafers andhas a focal point proximate to the first end so as to focus receivedsunlight into the optical wafer associated with the first end.
 11. Thesystem of claim 9, wherein the optical wafers comprise planar bodiesformed of a substantially transparent material.
 12. The system of claim9, wherein the absorber tube comprises a sidewall formed of materialthat is at least translucent to light and wherein the optical wafers arearranged such that a portion of the sunlight focused into the first endsis transferred via total internal reflection to the absorber sidewall.